"She was so young, she didn't even know," one mother told KBOI-TV.
A decade ago, her daughter was just five years old and already showing signs of developing.
"She went from an A-B cup to a D within about a year and put on about 80 pounds in the first year," she said.
For another mother, she also couldn't believe what was happening.
It began with a phone call from her 9-year-old daughter in elementary school, saying she started her period.
"You start thinking... it is her period?" she said. "She's only 9. And then I started thinking to myself, has somebody done something to her?"
Both mothers will tell you their first worry was how their young girls could possibly understand, or manage, this grown-up issue.
"Their body's telling them one thing, and their brain's like... I just want to play with Barbies, you know?" the mother of the 9-year-old said.
For the 5-year-old... her age was so young, doctors put her on medication to delay her period until age 10.
For several years, that meant expensive trips to clinics for monthly, sometimes weekly injections, up to $1800 dollars per visit.
"Well, it's hard," the mother said. "Because you kind of feel like you're playing God in this natural progression, and yet, my gut feeling all along was, this is not right."
On average, most girls start puberty around age 10 and their first period starts about 2 1/2 years later, around 12 1/2.
But these girls went through what doctors diagnose as precocious puberty, which means their development starts before the age of 8, includes breast buds and pubic hair, and, they can be menstruating and ovulating.
Doctors know what's happening to their bodies, but the question is why?
"The most common reason that I think makes sense is that we're having better nutrition now," said Dr. Juliana DiGiosia with Saint Alphonsus Regional Medical Center. "The steady source of calories and increased risk of obesity and that makes it more likely for girls to go through puberty earlier."
DiGiosia said the medical world agrees that girls are starting their periods earlier.
As of 2010, twice as many girls began early puberty compared to a decade ago.
But whether it's nutrition, man-made chemicals, or whether the two can be connected, remains in question.
What we do know: the FDA allows six hormones in the food supply, including testosterone and progesterone... sex hormones that can trigger puberty.
Another concern: toxins in household products, particularly parabens, that can act like estrogen and accelerate puberty.
And there's new research from Oregon Health and Science University.
Last month, scientists discovered when they manipulated protein levels in female rats, they could delay puberty.
Does it hold all the answers?
But doctors say it's another piece fitting into the precocious puberty puzzle.
For both mothers, the onset of early puberty is as much a mystery, as it is a curse.
"She was so much younger than a lot of her friends," said the mother of the 9-year-old. "I asked her, has anyone else had any of this going on? and she's like, 'I don't know, and I'm not asking'."
Both girls have since grown up.
The 9-year-old is now 15 and the 5-year-old is now 14.
But one still has the scars from growing up faster than she wanted.
"She still struggles a lot... I can't even go there," said the mother of the now 14-year-old.
Yet these two mothers forge on... with one message for anyone experiencing what they've already been through.
"It's their body, it should be their input," the mother of the 14-year-old said. "If you don't establish that kind of trust with them, they're not going to come to you for the important things like this."